This invention relates to control of internal combustion automobile engines, and more particularly to automatically controlling the idle speed of such an engine.
Because of present federal and state government rules and regulations, much work is being done in the automobile industry to control various aspects of automobile engine operation. Two major areas of work are fuel management and engine emissions. The former seeks to improve fuel economy while the latter attempts to reduce exhaust pollutants. Numerous control schemes have been employed to achieve both these goals (see, for example, U.S. Pat. No. 4,150,645 to Berent; U.S. Pat. No. 4,056,936 to Nakamura et. al; U.S. Pat. No. 3,963,009 to Mennesson; U.S. Pat. No. 3,738,341 to Loos) while at the same time retaining good engine driveability characteristics.
A common feature in most, if not all, of the various schemes is the controlling of the air-fuel ratio of a mixture produced in a carburetor or similar charge forming device and combusted in an engine. It is the conventional wisdom that by controlling air-fuel ratio for a wide range of engine operating conditions both improved fuel economy and reduced emissions are attained.
One portion of the range of engine operating conditions now being considered for control is engine idle speed. It is known that engine idle speed varies depending upon certain conditions; i.e. is the engine cold when first started; is the engine subjected to a load such as air conditioning while idling; does the engine run on (diesel) when shut down, etc.
Automatic engine idle speed control has two major benefits. First, it permits engine idle speed to be set lower than previously thus increasing fuel economy. Second, automatic idle speed control effectively tamperproofs the idle speed control of a carburetor thus preventing the idle speed setting from being adjusted after the engine has left the factory. Tamperproofing of various portions of a carburetor is a federal requirement for future automobile engines and the idle speed adjustment of a carburetor is one of the things required to be tamperproofed.
Until now, most automatic idle speed control schemes have employed a proportional control approach. That is, the system employed immediately responds to a sensed change in idle speed to attempt a correction back to a desired idle speed. While this approach permits some control over idle speed, it has problems. For example, not all engines operate the same way. That is, a four-cylinder engine responds differently than a six or eight-cylinder engine as does an in line engine from a V-engine. As a result, a system which is designed to produce satisfactory control over one type of engine is incapable of producing satisfactory control over a different type engine. What is needed is a single system capable of operating with a wide range of engines to obtain satisfactory idle speed control for each without a major modification being required to accomodate the system to each separate engine.